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RAM AIR: What's It Worth?

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  • RAM AIR: What's It Worth?

    Found this on the Net, so it must be true...B-)

    RAM AIR: What's It Worth?

    By Jon Doran

    Why are Kawasakis so damn fast? Anyone who's experienced the giggling
    buzz of a ZX's awesome acceleration from the pilot's seat comes away
    shaking his
    head in disbelief. Time after time the big K's machines run faster at
    the strip
    than rivals which put out notionally identical horsepower. So where do
    extra horses come from? This is an account of the first attempt to
    scientifically measure the real effect of ram air. The results may
    surprise you.


    The ZX-11, ZX-9R, later versions of the ZX-6 and ZX-7 and the new ZX-6R
    all utilize the ram-air system, and now Honda's latest CBR600F3 has
    along the same path-a sure sign that it works.

    The difficulty is in measuring the effect, simulating the results of a
    airflow, while the motorcycle is harnessed to a static dyno. But that
    is exactly
    what we set out to do with the help of Steve Burns, noted builder of
    special turbocharged, trick-framed motorcycles, sometime dragracer,
    endurance-racing-team boss and the owner of a Dynojet Model 100 dyno.
    As an
    innocent patient we had one meticulously prepared Kawasaki ZX-9R Ninja.


    In essence, the theory behind forced-induction systems like Kawasaki's
    is quite
    simple and not that far removed from turbocharging, just at a less
    level. A motorcycle traveling at high speed is pushing a slug of
    pressurized air
    ahead of it. If an air inlet is placed in the correct place, then air
    the airbox will be at greater than atmospheric pressure. The resulting
    charge will be denser and cooler and contain more oxygen and fuel, thus
    a bigger bang and hence-Hallelujah!-more power.

    There are limitations. The amount of mixture you can force through a
    motor is
    finite. Imagine strapping a ZX-9R on top of a jet aircraft and starting
    motor; the plane will rapidly reach a velocity where the motor would be
    incapable of utilizing the volume of mixture being forced into it.
    Next, at very
    high speeds-over say 150 mph, where theory says that ram air should be
    most effectively-the nature of air drag means that large increases in
    are needed to produce relatively small increases in speed. Finally,
    compared to
    a turbocharging system, the increases in pressure are quite low. How
    Before we began testing, Burns predicted, "I don't think we can get
    more than
    one psi in there."


    Kawasaki's ZX-9R uses a relatively straightforward system compared to
    the 1995
    Honda CBR600F3. Twin vents mounted beneath the headlight channel air
    via ducts
    running over the frame beams and into a sealed airbox. Look closely,
    and you can
    see two smaller nozzles behind the grilles which connect to the
    float bowls. Their function is to equalize the pressure between float
    bowls and
    airbox; without them the higher pressure of the incoming charge would
    upset the
    carburetion, potentially blowing fuel out of the bowls and tending to
    push fuel
    back down the jets, causing mixture leanness. Kawasaki uses much the
    same system
    in all its ram-air machines, though the ZX-7 and earlier ZX-11s have a
    inlet only.


    To reproduce the effects of high-speed running on a static dyno, Burns'
    intention was to use a fan capable of producing relatively small
    volumes of air,
    but at high pressure. The fan was connected via custom-made tubing and
    to the intake vents of the big Kawasaki. The joint was carefully
    sealed with
    high-density foam.

    So we could measure the pressures generated in the airbox as we pumped
    air up
    the ZX-9R's nostrils, a manometer, or pressure gauge, was plumbed into
    it. With
    the manometer we would be able to measure pressure up to 30 millibars
    atmospheric pressure. A bar is roughly equivalent to atmospheric
    pressure; one
    millibar (mb) is just one thousandth-0.001-of a bar. Not a lot compared
    to tire
    pressures, but Steve's experience with varying boost levels on his
    turbo-which churns out approximately an extra five horsepower for every
    70-millibar (one-psi) increase in boost or intake pressure-suggested
    that if it
    were possible to create one psi of pressure in the airbox, we could be
    at an increase of 5 to 6 bhp. Note that pressure, in the context of
    article, is pressure above atmospheric pressure.


    The ZX-9 runs air from the fairing's leading edge over the frame
    Other bikes, such as the ZX-6R, pass the fresh-air runners through
    the frame,
    while Honda's CBR600F3 breathes in fresh air from above the radiator
    and below
    the triple clamp.

    Burns' first thought was to set the air pressure at a certain level,
    say 15mb,
    and then measure the power at a steady throttle at 1000-rpm intervals.
    This was
    abandoned when we realized the results would be meaningless using CV
    which wouldn't necessarily be at full lift.

    The second problem was that as the slides lift and the motor drags in
    air, the
    pressure in the box drops off. Observation suggested that if the airbox
    was set to 10mb at idle, then at the redline, the manometer would show
    4mb. Obviously this bears little relation to real life, as the only way
    airbox would be pressurized at idle would be if the bike were
    freewheeling down
    the highway.

    Most importantly, the level of intake pressure on the road would be
    relative to
    the velocity of the motorcycle. If the airbox were pressurized to 20mb
    at 150
    mph, it would be correspondingly less pressurized at 120 mph and still
    less at
    70 mph. We had no way of reproducing this effect on the dyno, but if we
    show that an air pressure of, say, 20mb gave a boost of 3 bhp at a
    certain point
    in the rev range and could then relate that to real road conditions,
    we'd have
    a fair idea of what the actual power output on the road would be.

    In the longer term, Burns hopes to be able to use an interface between
    fan and
    dyno to take account of increasing air speed and thus simulate the
    effect of
    road speed on a static dyno.


    The initial step was to run the Kawasaki at atmospheric pressure-no
    boost-to get
    a baseline figure. The ZX-9R, like others tested on the same facility,
    gave 123
    bhp at its power peak. The induction fan was then connected, and the
    bike was
    run with the intake pressure set to 10mb at idle. The process was then
    with 20 and 30mb of pressure. In each case the intake pressure fell by
    approximately 6mb at peak revs when the slides were fully up and the
    engine was
    gulping down great gobs of mixture.

    The results were gratifyingly clear. At peak power the ZX-9R was
    producing an
    extra 2.6 bhp for every extra 10mb of pressure fed into it by the fan.
    power was up from 123 bhp to 131 bhp, an extra 8 bhp over atmospheric
    A secondary bonus was that the bike also hung on to its peak better,
    which would
    translate into a more forgiving motor on the road, which would be less
    sensitive to gearing and thus more likely to be able to take advantage
    following winds or favorable gradients to give a higher maximum speed.
    of the testing procedure we'd been forced to use, the graphs also
    showed similar
    increases right through the rev range, but this was obviously
    deceptive. There
    was no way that the levels of boost measured at low speed on the dyno
    could be
    reproduced on the road. At this point we suspected that boost would be
    insignificant at speeds below 100 mph.


    So far so good. The first part of the experiment was a success. We'd
    shown that
    pressurizing the ZX-9R's airbox definitely produced power increases.
    established that the system has the potential to work, but what we
    didn't yet
    know was how the pressures we'd managed to generate on the dyno-a
    maximum of
    30mb at idle, or 24mb at peak revs-related to real road conditions.
    Phase two
    was to attempt to establish what sort of pressures are actually
    generated in the
    Kawasaki's intake system at speed and relate them to the dyno results.

    Hidden but visible behind the black aluminum nets are the twin-snorkle
    pipes, which pressurize the carb float bowls to match the airbox.
    To reproduce the effect of a rapidly moving ZX-9, we pumped air up
    the Nine's
    nose with this attachment; the lower hose is the standard dyno cooling
    directed at the radiator. For an airtight fit, Steve Burns taped the
    intake hose
    in place and checked the pressure with a manometer.
    Motorcycle (Kawasaki ZX-9) speed and airbox pressure


    Had we been NASA or a top GP team, the next step would have been easy.
    Strap a
    datalogger to the bike, rent a private test strip and go play for a
    couple of
    days. We weren't, so the manometer was cunningly strapped to the gas
    tank, green
    food coloring added to the fluid for added visibility, and a portable
    datalogger-yours truly-mounted to the bars.

    Just riding from the dyno facility to the strip was illuminating. We'd
    on needing 90 mph before boost would register, but at an indicated 70
    mph the
    manometer already showed 8mb of boost.

    At the strip we were able to give the big Kwakker its head, with one
    eye on the
    slowly rising column of green fluid and the other on the rapidly rising
    At the end of each run we logged boost pressure against indicated

    The results were even better than we'd hoped for. At lower speeds
    (under 120
    mph) the gauge was easy to read and the results quite consistent: at 70
    pressure was 8mb; at 80 mph, 10mb; at 100 mph, 12mb; at 110 mph, 14mb.
    From this
    point things really took off: At 120 mph (indicated) the airbox
    pressure was
    approximately 19mb, at 130 mph about 23mb, at 140 mph, 26mb and at an
    150 mph, the gauge was beginning to pump out green liquid as it bubbled
    over the
    30mb limit.

    At a real speed of 167 mph, past experience shows that the ZX-9R's
    indicates 181 mph; there was obviously even more to come, perhaps as
    much as 30
    mph worth of additional air pressure. Plotting the air pressure figures
    speed for a rough representation of the way the air pressure increases
    that the progression isn't linear.

    This is as we'd expected. Air drag doesn't increase at a linear rate
    relative to the square of the speed. At above 25 mph, air resistance
    builds in
    proportion to the square of the air speed over the motorcycle: twice
    the speed,
    four times the resistance. The faster the bike goes, the greater should
    be the
    increase in pressure and thus intake pressure. When we plotted the
    rough course
    of the pressure increase on a graph and continued it upward, we came up
    with a
    projected 44mb (or more) of pressure at an indicated 180 mph, when the
    would actually be traveling at its real top speed of 167 mph.


    The maximum pressure we were able to generate on the dyno was
    30mb, which gave a peak of 131 bhp from a ZX-9R as compared to the 123
    measured at rest. In other words, each 10mb increase in inlet pressure
    is worth
    approximately 2.6 bhp at peak on a derestricted 9R.

    At an indicated 150 mph on the road, the inlet pressure had already
    neared the
    30mb figure. We can therefore say with confidence that the ZX-9R is
    producing at
    least 131 bhp at the rear wheel in real world conditions-8 bhp more
    than at
    rest on the dyno.

    Flat out, however, the Ninja indicates another 30 mph on the speedo. If
    boost at
    this speed was, as seems likely, 40mb, then the gain over atmospheric
    would be approximately 11.5 bhp, giving a peak figure of 134.5 bhp. If
    pressure reached 45mb, which it might well do, then the increase would
    be as
    much as 12 bhp, or a peak of 135 bhp. In other words, 123 bhp measured
    on a static Dynojet rolling road dynamometer could translate to as much
    as 135
    bhp or more on the street. Ram air works.


    The manometer wasn't eye-pleasing once taped in place, but it worked
    measuring pressure in the airbox at simulated speeds up to 150 mph.
    pressure gauge allowed us to quantify the effect of Kawasaki's ram-air
    system in
    the real world.
    Kawasaki ZX-11 D ram-air intake system.
    This magnification of the dyno chart shows the difference between
    dynoing a
    ZX-9 with ambient pressure (lower line) and then stuffing 30 millibars
    of wind
    into the intake system-a gain of eight horsepower (from 123 to 131 at
    the peak).
    The manometer shows that the ZX-9 reaches 30 millibars of airbox
    pressure at
    150 mph.

    An extra 12 bhp sounds like an extraordinary power gain for nothing
    except a bit
    of wind, but it's important to remember that at lower speeds the
    won't be as significant. Up to 120 mph when the boost hits 20mb, we're
    talking about the odd bhp. From then on it gets progressively stronger.
    As the
    effect is speed relative, it's at its most pronounced at very high
    the faster you go, the stronger the boost. But, hey, how many of you
    ride at 150
    mph on the street? Never mind, don't answer that.

    Having said that, the effects of even small amounts of boost on
    response haven't really been investigated and may help to explain some
    of the
    surging acceleration typical of big Kawasakis.

    It does, however, clarify the impressive figures that Kawasakis deliver
    at the
    strip and explain why a ZX-7 putting out the same power as a GSX-R on a
    dyno will romp away under speed testing. It also begs the question of
    someone is going to bring out a fully functional aftermarket

    Finally, it explains why Honda's jewellike CBR600 has finally gone the
    route in its quest to head off the ZX-6R.

    This story was originally published in the August 1995 issue of Sport
    Aim high and consider yourself worthy of great things

  • #2


    • #3
      By the time I read through all that shit above RAM AIR will be obsolete !!


      • #4
        Damn dood.. what the fuck do you do for your job? sit around and look at websites to see if the content is 'safe' or some shit like that??
        Right now Im having amnesia and deja vu at the same time. I think Ive forgotten this before.


        • #5
          Damn dood.. what the fuck do you do for your job? sit around and look at websites to see if the content is 'safe' or some shit like that??
          Yeah... sure... That's right... I check sites for 'safe' content. That's why I have to keep comming back here - havn't found any yet... :roll:
          Aim high and consider yourself worthy of great things


          • #6
            damn right BigW


            • #7
              i gotta get ram air for the XR...ill get wicked speeds from it
              I was raised on the Dairy....Bitch


              • #8
                Thanks for the infomation..

                Next time a lil girly gets of the zx7 and points t the intake and goes ... "wot are these" ill be able to start quotin some funky stuff

                Nick :twisted:


                • #9
                  I wouldn't Nick !!! I would offer her the term "Ram" alright but not in front of the bike....


                  • #10

                    nice one gordo
                    Nick :twisted: